This invention relates to a high voltage thyristor valve 30 accommodated in a valve hall 32 including a thyristor valve body 38 with a tower-like multiple valve structure erected upright on the floor of said valve hall.
Of high voltage thyristor valves (hereinafter referred to merely as a thyristor valve except for the abstract and claims of this application), an air insulating type used for DC transmission and for frequency converters is disposed in a house usually called a valve hall. This type of the thyristor valve is usually comprised of a high multi-layer structure, i.e. a tower type, with a minimum floor area which permits a saving of a floor area and a low-cost construction work thereof and facilitates the inspection and maintenance service thereof.
FIG. 1 is a plan view showing a type of power equipment which comprises the conventional three single-phase thyristor valves 10a, 10b and 10c, erected upright on the floor of a valve hall 12 and connected to respective phases of a three-phase wiring, main buses 14 connected to these thyristor valves, bushings 16 supporting the main buses, and a transformer 18 connected to the main buses. FIG. 2 shows an elevational view of the power equipment shown in FIG. 1. FIG. 3 shows an essential part of the electric wiring of the same power equipment. In FIGS. 1 and 2, the ceiling and one side wall of the valve hall 12 are removed to clearly illustrate the arrangement of the thyristor valves and related components.
Each of the thyristor valves 10a to 10c consists of four valves 20a (FIG. 2), they are called quadruple valves, which are stacked one above another into a tower-like form. Each valve 20a includes a predetermined number of thyristor modules. The thyristor valve 10c for one of the three phases, shown in FIG. 2, has a four-valve stacked structure. Each valve 20a shown in FIG. 2 is called a single valve and has a space in which are accommodated a plurality of units, called thyristor modules 40 (FIG. 4), which accommodate thyristor elements and associated circuits.
Shown enclosed in double-dash-bar rectangles 10a to 10c in FIG. 3, are electric circuits of the thyristor valves, 10a to 10c in FIG. 1, having the tower structure. The single valves 20a shown in FIG. 2, each consisting of a plurality of units called thyristor modules, are generally indicated at 20 in FIG. 3. They are called arms in the electric circuit nomenclature.
The transformer 18 shown in FIG. 1 is shown as two transformers 18a and 18b in FIG. 3 to clearly illustrate the wiring.
The individual single valves 20a shown in FIG. 2 each have an upper and lower frame so that they can be stacked one above another into the thyristor valves 10. Between the upper and lower frames of the single valve 20a is applied a high voltage which is carried by the arm 20 shown in FIG. 1. Therefore, the supports for the upper and lower frames of a single valve must have high insulation capacity and also have sufficient mechanical strength to support the thyristor valves stably and reliably. The mechanical strength must be sufficiently high to prevent the inconveniences as set out below.
(1) The thyristor valve swings toward the nearby apparatus to cause a dielectric breakdown and, in the worst case, it comes into collision with the apparatus to cause a damage.
(2) It is therefore necessary to construct a larger valve hall.
(3) The breakage of a electric lead wire connected to the thyristor valve may occur when it is stretched tight.
(4) Since the thyristor valve greatly swings at its top portion, a bending moment is exerted on the base portion of the thyristor valve, causing a damage there and a resultant overturning.
The supports noted above are usually made of epoxy resin insulators or fiber reinforced plastics (FRP). These insulators and FRP generally have low mechanical strength as compared with metals. If it is intended to reinforce the supports consisting of the insulator or FRP by increasing their size, their weight is undesirably increased.
The vibrations that would be experienced by thyristor valves of the tower-like structure when an earthquake occurs, will now be described by taking the thyristor valve shown in FIGS. 1 and 2 as an example. If the rated voltage of the thyristor valve of the tower-like four-valve (quadruple valve) structure shown in FIGS. 1 and 2 is 250 kV, the thyristor valve would have a height of substantially 11 m because of the necessity of providing a considerably large insulating distance between adjacent single valves. Studies have been made on the vibrations experienced by such a thyristor valve using a numerical analysis method. Generally adopted anti-earthquake standards for power equipment prescribe that a thyristor valve should not be damaged but continue normal operation when it experiences a horizontal vibrating force due to three cycles of a sinusoidal wave with an amplitude acceleration of 300 gal and at the same vibration frequency as its specific frequency. Dimension D1 of the insulator, which is necessary for satisfying this requirement, has been calculated. In addition, dimension D2 of the insulator, which is necessary for satisfying the requirement noted above for a thyristor valve, which consists of only a single valve corresponding to the single valve in the thyristor valve shown in FIG. 2, with a rated voltage of 125 kV, has been calculated. It has been found that D1 is substantially double D2, and the weight in the former case is approximately four times the weight in the latter case. According to the results of the numerical analysis described above, a higher vibratory acceleration is exerted to a higher portion of the thyristor valve. With the thyristor valve of the tower-like four-valve structure with a rated voltage of 250 kV, the acceleration exerted to the top is approximately eight times the acceleration exerted to the top of the solitary single valve with the rated voltage of 125 kV. The amplitude of vibration at the top of the thyristor valve with the rated voltage of 250 kV is as large as approximately 60 cm. Since the lower end of the thyristor valve is installed on the floor, when its top is vibrated, a great bending moment is applied at its lower end as in a cantilever, which is fixed at one end and has the other end free. Thus, a great bending stress is undesirably produced at the lower end.
Meanwhile, thyristor valves have become extensively used for power transmission equipment, and there is a trend for increasing the rated voltage and the capacity of thyristor valves and hence increasing the height and weight thereof. For this reason, there is an increasing demand for safety against vibrations, particularly earthquakes. To meet thus requirement, the size of the support has to be increased so long as the prior art structure as described above is adopted. Doing so leads to increased size and weight of the thyristor valve as a whole. Development of of a new method for solving this problem, therefore, has been demanded.